1. Field of the Invention
This invention relates to compound change gear transmissions of the type comprising a multispeed main transmission section connected in series with a multispeed auxiliary transmission section and in particular to compound change gear transmissions wherein the main section utilizes manually engaged nonsynchronized, unblocked jaw clutches to selectively engage a selected main section ratio gear and wherein the auxiliary section utilizes blocked resiliently shifted jaw clutches to selectively engage a selected auxiliary ratio. Preferably, the blockers and associated clutch members in the auxiliary section have complementary ramps on the blocking members thereof configured to prevent nonsynchronized engagement of the associated jaw clutch members when the main section is engaged but which will tend to act as positioners to place the blocker and clutch member in a nonblocking condition when the main section is in a neutral or disengaged condition.
2. Description of the Prior Art
Compound transmissions of the splitter or range type or a combination thereof, are well known in the prior art as may be seen by reference to U.S. Pat. Nos. 3,105,395; 3,648,546; 3,799,002; 2,932,988 and 3,229,551, all hereby incorporated by reference.
Blocked change gear transmissions of both the single and the compound types are also well known in the prior art as may be seen by reference to U.S. Pat. Nos. 3,799,002; 3,921,469; 3,924,484; 3,983,979; 4,192,196 and 4,194,410, all of which are hereby incorporated by reference.
In the design of transmissions, particularly heavy duty transmissions, such as used in trucks, there has existed for a long time the problem of shifting the transmission to the various speed ratios, which problem is even greater when the transmission is compounded, that is provided with an auxiliary transmission section of the range or the splitter type for increasing the number of speed ratios. In most known transmissions, the shifting process is either relatively difficult and/or the shifting mechanism is relatively complex. Thus, there has been a continuing effort in the design of transmissions to improve the shifting, to improve the rapidity of shifting, to reduce the complexity of the shifting mechanism, and to reduce its weight, space requirements and costs. Hence, without detracting in any way from the operability or desirability of many of the shifting mechanisms previously known, it may be stated that in the present invention these general objectives are accomplished to even a greater degrees than has been previously possible.
Particularly, most previously known transmissions have required a relatively high level of operator skill or necessarily utilized synchronizers, of which many different types are known, for causing the speed of the jaw or tooth clutch members to be substantially synchronized prior to permitting their interengagement during a shifting sequence from one speed ratio to another speed ratio. While the use of synchronizers does permit the shifting operation to be performed, their use, as is already known, imposes certain requirements of weight, space and power which is desirable to ease, or avoid entirely, if possible. This problem has been minimized, but not eliminated, in known compound transmissions wherein only the auxiliary section is provided with synchronizing means.
Blockers of the type described and illustrated in the above mentioned U.S. Pat. Nos. 3,799,002; 3,910,131; 3,921,469 and 3,983,979 are generally nondeformable devices designed to prevent, or block, the engagement of the axially engageable jaw clutch members of a jaw clutch when said members are rotating at substantially different speeds, i.e. are not substantially synchronized. Transmissions utilizing such blockers are referred to herein as "blocked transmissions". Blocked transmissions are transmissions utilizing blockers to prevent jaw clutch engagement if the members of the jaw clutch are not substantially synchronized. This is in contrast to "synchronized transmissions" which utilize synchronizer clutches to cause the jaw clutch members to be synchronized. The relatively nondeformable blockers utilized with many of blocked transmissions of the prior art are generally retained on one clutch member for rotatin therewith with a limited amount of relative rotation (3.degree.-15.degree.) provided. The blocker and the one clutch member will define an array of projections or the like which will allow the one clutch member to move relatively axially toward the other clutch member when in alignment but will block such relative axial movement when said blocker is rotated in either the clockwise or counterclockwise direction relative to the one clutch member. The blocker is designed to be in positive frictional contact with the second clutch member during an engaging operation and will thus tend to rotate with the second clutch member. Random frictional contact will usually cause the blockers to rotate with the second clutch members at times when a clutch engagement is not attempted.
By way of example, assuming the use of a relatively nondeformable blocker as disclosed in the above mentioned prior art and that the clutch members are rotating in a clockwise direction, if the first clutch member is rotating faster than the second clutch member, upon initiation of an engaging operation the blocker will be rotated counterclockwise relative to the first clutch member and the blocker will prevent axial movement of the first clutch member towards the second clutch member. If the second clutch member is rotating faster than the first clutch member, the blocker will be rotated clockwise relative to the first clutch member and the blocker will prevent axial movement of the first clutch member towards the second clutch member. If the first clutch member initially rotates faster, then slower than the second clutch member, the blocker would, relative to the first clutch member, rotate in a clockwise direction from an initial counterclockwise rotated position relative to the first clutch member towards a relatively clockwise rotated position. During the relative rotation, for at least a limited period of time, the blocker would align with the first clutch member and cease to block axial movement thereof towards the second clutch member. Such movement of the clutch members and the blocker is generally referred to as a "passing through synchronous" or "crossing synchronous" as the two clutch members reach a substantially synchronous rotation, and the clutch engaging operation, or the gear shift, should be completed at this time. As the blocker is designed to be in positive frictional contact with the second clutch member only during a clutch engaging operation to prevent undue frictional wear, it is possible, under certain conditions, that the blocker can be set up on the "wrong side of synchronous" at the initiation of a clutch engaging operation, i.e. referring to the above example, rotated clockwise relative to the first clutch member when the first clutch member is rotating faster that the second clutch member or vice versa. Under such conditions, especially if the driven device is stopped, it is often difficult or impossible to cause the blocker to "pass through synchronous" and the transmission cannot, without undue manipulation, be shifted into the desired gear ratio.
In a blocked transmission, the blocker clutch members have an inherent problem of achieving engagement under certain static conditions, i.e., when the driven device is standing still. When a blocked transmission of the twin countershaft type as is illustrated in U.S. Pat. No. 3,799,002 or 3,924,484 is in neutral with the master clutch engaged, the gearing will, for at least a period of time, rotate while the output or main shaft is stationary. This tends to place the blockers in the "upshift position", i.e., that position associated with a dynamic upshift wherein the jaw clutch member rotating with the mainshaft must be rotated faster than the clutch member rotating with the gearing to cause the clutch to pass through synchronous. When the gearing comes to a stop, the blockers remain in the "upshift position" and, because it is difficult to rotate the mainshaft with the transmission in neutral, a reversing of the gearing or an auxiliary aligning of the blockers is required to achieve a clutch engagement.
In a compound, blocked transmission of the type seen in U.S. Pat. Nos. 3,799,002 and/or 3,924,484 relative overspeeding of the auxiliary transmission gearing by the mainshaft can be achieved by the operator momentarily shifting the transmission from neutral into reverse. This method is possible as reverse is normally not a blocked gear. But this is obviously an inconvenience, a highly undesirable technique, and might hamper the commerical acceptability of an otherwise highly successful transmission.
Various types of self-aligning blockers, when utilized with an input shaft brake, are an effective auxiliary method of obtaining clutch engagement at a static condition. However, due to manufacturing, space, cost and operational considerations, an improved means for achieving status clutch engagement is desirable.
One attempt to minimize the problems of a fully blocked transmission involves the use of a selectively actuated mechanism to decelerate and/or reverse rotate the input gearing as may be seen by reference to U.S. Pat. No. 4,194,410. Although such devices have proven to be functionally acceptable, they do add additional cost and weight to a transmission utilizing same.